1. Field of the Invention
The present invention relates to a data processing device such as an IC (Integrated Circuit) card, and more particularly to a data processing device having a connection terminal for a wired connection and an antenna for a radio connection and switchable between the use of the connection terminal and the use of the antenna, and a method of controlling operation of the data processing device.
2. Description of the Related Art
IC cards are available as one type of portable data processing devices. IC cards are widely used in many applications as prepaid cards for public telephone sets, identification cards for entering and leaving rooms, and mediums for electronic money. An IC card comprises an integrated circuit made up of a microprocessor, a memory, etc. and embedded in a plastic card. There have been developed three types of IC cards, i.e., contact cards, contactless cards, and combined cards, that are selectively used depending on the form of signal and power transmission to and from an external circuit.
The contact IC cards have a plurality of exposed connection terminals. When a contact IC card is inserted into a card reader, the connection terminals of the contact IC card are brought into direct contact with connection terminals of the card reader. The card reader and the contact IC card are now electrically connected to each other, allowing drive electric power to be supplied from the card reader to the contact IC card and also allowing various signals to be transmitted between the card reader and the contact IC card, so that the microprocessor in the contact IC card can process data.
The contactless IC cards have a radio antenna rather than exposed connection terminals. The radio antenna is used to send various signals to and receive various signals from the card reader via a radio wave or electromagnetic wave. The radio wave from the card reader is also used to send electric power as well as signals to the contactless IC card. The IC card extracts the signals and the drive electric power from the radio wave that is received by the antenna.
The combined IC cards have a combination of the functions of contact and contactless IC cards. The combined IC cards have both a plurality of exposed connection terminals and an antenna. A combined IC card is selectively operable in two switchable modes, i.e., a terminal mode in which it operates in the same manner as the contact IC card and an RF (Radio Frequency) mode in which it operates in the same manner as the contactless IC card.
The contact IC card provides better security than the contactless IC card because signals are exchanged between itself and the card reader through a wired connection. The contactless IC card can be handled more easily than the contact IC card since the contactless IC card is not required to be inserted into the card reader. The combined IC card can be handled easily and provides high security as it can transmit data requiring less security via a contactless connection.
As described above, the combined IC card needs to be switched between the terminal mode and the RF mode. Japanese laid-open patent publication No. 3-209592 (JP, 03209592, A) discloses that the voltage level of drive electric power applied to one of connection terminals and the voltage level of drive electric power extracted from a radio wave supplied from the antenna are compared with each other, and one of the terminal mode and the RF mode is selected based on the result of the comparison. Since the voltage levels are generally compared with each other by an analog circuit such as a comparator for mode switching, the mode switching process is performed under analog control. The mode switching process under analog control is problematic in that it is not a clear-cut process. Specifically, control conditions for mode switching tend to vary due to errors and variations in diffusing conditions in the fabrication of semiconductor integrated circuits contained in the combined IC card.
In actual usage of the combined IC card, when electromagnetic noise is received by the antenna, the mode of operation of the combined IC card may possibly switch to the RF mode unexpectedly. If the user, not knowing that the combined IC card is in the RF mode, inserts the combined IC card into a terminal-mode card reader, then the combined IC card may possibly malfunction. Alternatively, even if the combined IC card inserted in a terminal-mode card reader normally operates in the terminal mode, the mode of operation of the combined IC card may switch to the RF mode due to extraneous electromagnetic noise, causing the combined IC card to suffer malfunctioning.
In order to prevent such malfunctioning, the combined IC cards are designed with care not to operate with radio inputs that do not meet IC card standards. However, because a portable terminal-mode card reader is available in the art, a combined IC card thus designed may still be caused to malfunction when the user inserts the combined IC card into such a portable terminal-mode card reader that is carried by the user, without recognizing the presence of an RF-mode card reader that is installed nearby.
As described above, when an input is applied to the antenna of a combined IC card and an input is also applied to the connection terminals thereof at the same time, those simultaneously applied inputs may cause the IC card to malfunction and fail. The manufacturer of the combined IC card cannot identify the cause of such malfunctioning and failure because the manufacturer finds it difficult to confirm the environment in which the user uses the combined IC card.
In the RF mode, the combined IC card extracts drive electric power from a received radio wave. Therefore, when excessive electromagnetic noise is applied to the antenna, it may produce an unduly high drive voltage which tends to destroy the internal circuit of the IC card. One solution is to insert a shunt regulator in the supply path of drive electric power in the combined IC card. However, the shunt regulator is disadvantageous in that it wastes part of the drive electric power that is stably supplied from a connection terminal when the combined IC card is in the terminal mode.
General combined IC cards have an RF circuit for processing signals that are supplied via the antenna in the RF mode. The RF circuit has such characteristics that when the drive voltage thereof is higher, the communication range of the RF circuit is smaller. For this reason, if a combined IC card extracts a high drive voltage from a signal supplied via the antenna, then the high drive voltage is reduced to a predetermined voltage by a shunt regulator. The combined IC card has a common feeding path for drive electric power supplied from the antenna and drive electric power supplied from a connection terminal. Consequently, the shunt regulator causes an unnecessary voltage drop in the drive electric power supplied from the connection terminal. This problem may be solved by turning on the shunt regulator in the RF mode and turning off the shunt regulator in the terminal mode. However, it is difficult to protect the internal circuit of the combined IC card reliably while preventing an unnecessary voltage drop because extraneous electromagnetic noise may possibly be applied via the antenna while the combined IC card is operating in the terminal mode.